1. Technical Field
This application relates generally to the field of lighting. More particularly, this application relates to the technology of controlling electrical loads, such as the intensity (i.e., dimming) of lighting sources.
2. Background Information
Presently, there are a variety of lighting sources in widespread commercial use. Some popular examples include incandescent, fluorescent, and solid state (e.g., light emitting diode (LED)) lighting sources. Even within certain lighting categories, there can be further distinctions, such as incandescent lighting operating at AC line-voltage levels (e.g., 120V, 60 Hz), or at DC low voltage (e.g., 6, 12, or 24 volts). Lighting sources operating at DC low voltages can be further distinguished into those using magnetic transformers and those using electronic (e.g., solid state) transformers. LED lighting sources typically require a matched LED driver, or power supply, providing the appropriate driving current and voltage levels dependent upon the nature of the LED lighting source.
In many lighting applications it is desirable to provide some measure of control to allow for variability of one or more attributes of the lighting source beyond simply “on” and “off” For example, a dimmer control can be provided to otherwise control the power delivered to the lighting source to achieve desired illumination intensity. Each type of lighting source (load types) has individual characteristics that generally require special types of dimmers. It is important to use a dimmer that is designed, tested, and UL listed for the specific lighting source/load type.
Dimmer controls can be user accessible, for example, as in wall switch styles providing a user adjustable control, such as a rotary knob, a sliding switch and electronically controllable switches (e.g., capacitively coupled). A user adjustment of the control is automatically converted by the dimmer into a corresponding power adjustment, for example, allowing a continuous adjustment of the resulting illumination from a maximum power (e.g., 100% or full on) to a minimum power (e.g., below 10% or off). As a consequence of fundamental differences between the various lighting sources, a dimmer for one might not work with another. Thus, a dimmer control suitable for incandescent lighting may not be suitable for fluorescent or solid state lighting sources.
One such class of dimmer controls is referred to as TRIAC (triode for alternating current) dimmer controls. Basically, TRIAC based light dimmer circuits “chop up” the sine wave voltage, that is, removes portions of the sine wave waveform so that the average voltage and thus the average power passed to lighting system is reduced, thereby reducing the emitted power of the lighting system. Such devices are typically used for incandescent lighting applications. At its full brightness setting, the TRIAC dimmer control allows most, if not all, of the AC power waveform to pass through it, to power the light. As the dimmer control is adjusted to a dimmer setting, a greater proportion of each AC power cycle is chopped proportional to the position of an internal potentiometer. A dimmer setting results in a lower average (e.g., RMS) power over the period, resulting in corresponding reduction of illumination output.
Unfortunately, such “chopping” of the voltage and current waveforms, which introduces rapidly changing transients and waveform edges into the “chopped” waveform, results in the generation of undesired high frequency components into the waveform, resulting in radio frequency noise and interference. In lighting systems, rapid transients and waveform edges in the power waveforms further effect elements of the system, such as filaments of a bulb, causing such elements of the system to vibrate and causing an undesired buzz to emanate from the bulb or the lighting system. Moreover, such “chopping” is not well suited for all lighting sources.
TRIAC dimmer controls are generally not well suited for LED lighting sources. Such solid-state lighting applications generally include a power supply converting facility AC power to power suitable for the solid state lighting. In particular, for LED lighting the direction of current as well as its amplitude are controlled by such a power supply to provide desired illumination. As such, digital lighting applications are typically isolated from the AC mains by the presence of such a driving power supply. Accordingly, there is no assurance that providing a TRIAC chopped AC signal to a driving power supply associated with solid state lighting will result in the intended illumination setting, or dimming. In fact, there is no assurance that the solid state lighting will even operate as intended when powered by such a chopped AC waveform.